Manufacture of motor fuels



Febyl, 1944. L. A. CLARKE ,ETAL 2,340,412

MANUFACTURE OF MOTOR FUELS Filed March 8, 1939 STABILIZER SETTLER ABSORBER Louls A. CLARKE FRANK H.BRuNEa ERNEST F. PEVERE' GEORGE B. HATCH INVENTORS FRACTIONATORV Wig/ ATTORN EYS Patented Feb. 1, 1944 MANUFACTURE OF Moron. FUELS Louis A. Clarke, Fishkill, and Frank Henry Brun- .er, Ernest F. Pevere. and George B. Hatch, Beacon, N. Y., The Texas assignors, by mesne assignmentsfito Company, New York, N. Y.. a corporation of Delaware Application March 8, issas rialna'zsonso 8 Claims.- (01. 260-683.4)

This invention relates to the manufacture :of motor fuels such as gasoline and has to do particularlywith the production of high antiknock saturated gasoline hydrocarbons by the alkylation or condensation of low boiling isoparaflins, for example isobut-ane and isopentane, with olefins 01' polymers thereof in the presence of concentrated sulfuric acid as a catalyst.

The alkylation of low boiling isoparaflins,-such as isobutane r isopentane, with C4 olefins or a mixture of C4 and C3 olefins takes place readily in the presence of concentrated sulfuric acid of about 90 to 98% strength, and preferably about 94%, when the amount of isoparaifins is in excess of that of the olefins. preferably between three and five times that of the olefins by weight, at ordinary temperatures, for example 50 to 90 F. in the liquid phase.

The propylene containing hydrocarbons, which have been proposed for alkylation heretofore,

have contained relatively large amounts of C4.

olefins. For example, cracking still gases or refinery gases, ordinarily contain as much C4 as C: olefins, and often the C4 olefins are in considerable excess, such as twice the amount of: the propylene.

It is often important to be able to alkylate C3 olefins containing considerably smaller amounts of C4 Olefins than contained in ordinary refinery products. Thus gaseous products from special processes such as catalytic polymerization, dehydrogenation of propane, special fractionation, etc., may contain essentially propylene as the olefin constituent. Higher temperatures of the order of 120 F. or over have been heretofore thought optimum for the sulfuric acid alkylation of isoparafiins with propylene, or with olefinic fractions predominating in propylene.

It has now been found that low boiling isoparaffins can be alkylated with propyleneunder 1 substantially-the same temperature conditions as usedwhen alkylating C4 olefins if a'small amount of a butylene is present as a promoter of the alkylation reaction. The amount .of butyl'cne present should :be between about 5% and and preferably about 10% by weight of the propylene. This proportion range of the promoter is critical and it is the discovery of this critical proportion range that is an important improvement in the art.

Either isobutylene or normal butylenes, 0r polymers of isobutylene or normal 'butylenes, may be used as promoters. It has been found, however, that isobutylene is somewhat, more effective as an activator than normal butylenes. For example, the alkylation reaction of propylene takes place in the presence of 10% of isobutylene. at a temperature :of about F. whereas with 10% of butylene-2 a temperature of to F. isurequired. As illustrating the effect of varying percentages of isobutyleneon the reaction, 5% requires a temperature'of about F., 10% atemperature of about 65 F. and 15% a temperature of about 60 F. to secure optimum yields of desired product.

For purposes of illustration, there is set forth below data obtained by the alkylation of isobutane with propylene alone and propylene in the presence of isobutylene.

90% propyl- Olefin charge gig ene, 10% Hwy! isobutylene ene Isobutane to olefin ratio 3.1:1 2. 7:1 3. 3:1 Per cent concentration of sulfuric acid 98. 3 98. 3 98. 3 Acid to hydrocarbon dosage. 2.1:1 1. 851 2. 2:1 Temperature F 65 68 Time of addition of olefins i minutes. 60 6O 60 Additional reaction time minutes. 30 30 30 Per cent by weight of debutanized liquid, basis of olefln 78. 6 220. 2 215. 5 Material balance 98.3 99. 3 99. 9 Per cent H2804 in recovered acid 58. 0 95. 7 88. 4 311 F. E. P. fraction:

Per cent yield by weight,

basis of olefin F5. 5 185.9 164.1 Octane number 0. F. R. M. 88:5 85. 3 Bromine number 1 1 1 From the .above data it will be observed that it is. necessary to operate at about 120 F. to obtain a good yield of alkylation product when reacting isobutane with propylene alone. The results obtained by using a small amount .of isobutylene as a promoter, however, even at -68 are much superior .to the results obtained when using propylene alone, .even at the higher temperatures. Thus the yield of 311 F. end point product when using a mixture of 90% propyleneand 10% butylene is 185.9% as compared with 65.5% when operating .under the same conditions with proylene alone and 164.1% when operating with propylene alone at 120 F. Moreover, acid deterioration is minimized with the activated mixture.

Further objects and advantages of the invention will become apparent to those skilled in the art from the following description of the invention-wherein reference will be made to the accompanying drawing showing one form of apparatus for carrying out the process of the invention.

Referring to the drawing, an unsaturatedgaseous hydrocarbon mixture, such as a refinery gas, comprising mainly C3 and C4 hydrocarbons, is charged through the line I to a fractionator 2. The hydrocarbons are fractionated to separate overhead a C3 fraction containing a substantial amount of propylene, a side stream consisting primarily of isobutyane and C4 olefins and substantially free from normal butane, and bottoms comprising the remainder of the C4 fraction.

which contains substantially all the normal butane. ene-2 and normal butane, the fractionation described above necessarily removes most of the butylene-2 along with the normal butane. The side stream containing the isobutane necessarily includes most of the isobutylene and butyiene-l with th isobutylene predominating. The bottoms containing normal butane are withdrawn from the lower portion of the fractionator through the line 3. from the upper portion of the fractionator through the line 5 and introduced into an absorber' 6. The gases in the absorber 6 are scrubbed with sulfuric acid to absorb the propylene. The'unabsorbed gases comprising propane are released from the top of the absorber through the line'l, and may be passed to a propane dehydrogenation plant (not shown) from which the produced propylene-propane mixture may be charged to the absorber 6. The propylene acid mixture is withdrawn from the lower portion of the absorber through the line 9 and forced by the pump l through the line H to a're'actor l2. 'The feature of absorbing a low-boiling olefin such as propylene in sulfuric acid followed by alkylation of the acid-olefin product with a low-boilin isoparaflin is disclosed and claimed in copending application, Serial No. 215,736, filed June 25, 1938.

The acid used in the absorption of propylene in absorber 6 is concentrated sulfuric acid of about a 98% strength, which is introduced through the line H and forced by the pump l through the lines I6 and I! into the upper portion of the absorber. While only one absorption tower is shown in the drawing, it is to be understood that two or more towers may be used.

The method of the acid absorption of the propylene from the C3 fraction may vary. Ac-

cording to one method of operation the amount of propylene absorbed can be regulated to produce a substantially saturated solution of propylene in the acid. Another method of operation is to control the acid absorption so that a comparatively dilute solution of propylene andstrong acid is obtained. It is preferable to carry out the operation according to the first method whereby there is less difficulty involved in the control of the absorption operation. v

7 If a substantially saturated solution ofpropylone and acid is produced, then it is desirable to charge this rich absorbent mixture to an alkylation zone containing a quantity of additional fresh acid of alkylation strength to cause the propylene to enter into the alkylation reaction in the presence of theCr olefin promoter. This additional acid may be introduced into reactor 12 through the lines and 22, or'mixed with the acid absorbent mixture in the line I I through the branch line 2| and the mixturethen passed into reactor l2. In starting up the plant, it is desirable to first saturate this additional acid with isobutane and start feeding C4 olefin before introducing the propylene-acid solution. If a dilute solution of propylene in the acid is obtained in the absorber, then it may be unnecessary to add The C3 fraction is withdrawn Due to the close boiling points of butyl additional acid providing there is suificient excess acid in the absorbent mixture to meet the requirements of sulfuric acid as a catalyst in the alkylation reaction in the reactor I2.

The side stream containing C4 olefins and isobutane, referred to heretofore, is withdrawn at an intermediate point through the line 25 containing a pump 26 and passed to the reactor l2. The amount of the side stream is regulated to provide sufiicient C4 olefins to activate the alkylation of the isobutane with the propylene in the acid absorption mixture. Since the C4 olefin content of the said side stream consists predominantly of isobutylene, the increased promotional effect of this iso-olefin' is thereby obtained in a convenient manner. This amount should come within the critical range of about 5 to 15% of the propylene as referred to heretofore. The feature of absorbing propylene from a C3 hydrocarbon fraction in 253,052, filed January 27, 1939, now Patent No.

2,269,302, dated Januar 6, 1942.

It is preferable to maintain an excess of isobutane in the reactor [2, for example a ratio of isobutane to olefins of between about 3:1 and 5:1 or overyalthough as low a ratio as about 1:1 may be used. The amount of isobutane contained in the side stream withdrawn from the fractionator 2 is usually insufiicient for this purpose and it is ordinarily necessary to add extraneous isobutane which may be done through the line 28.

In the reactor 12 the acid and hydrocarbons are intimately contacted by suitable agitation, such as with a stirrer 21. Sufficient pressure is maintained on the reactor to retain the hydrocarbons substantially in the liquid'phase. A temperature of about to F. and preferably about 65 F. is used, although temperatures from zero to F. maybe used. A time of reaction of about 30 to 60 minutes and preferably about 45 minutes is required.

The reaction products are transferred from the reactor l2 through the line 29 to a settler 3|) wherein the used acid is allowed to settle out in the lower portion thereof and may be withdrawn through the line 3!. It is preferable to recycle a portion or all of the used acid by the pump 32 through the line 33, either to the reactor 12 through the branch line 35 or to the absorber through the branch line 36 and lines l6 and II. A portion of the used acid may be recycled to the reactor [2 or absorber or both, while suflicient of the used acid is withdrawn from the system for recovery, and an equivalent amount of new acid added to maintain the acid in the system at the desired concentration. The feature of absorbing a, low-boiling olefin in sulfuric acid, then alkylating the acid-olefin absorption product with a lowboiling isoparaifin in the presence of strong su1- furic acid of alkylation strength, and recycling used acid from the alkylation step to the absorp tion step is disclosed and claimed in the aforementioned copending application, Serial No;

The hydrocarbons separate out in the upper tion mixture-isitransferred from the mixer!!!- 1 91411 through the line to a settler 44 wherein the neutralizing agent is allowedto'settle out and is withdrawn through the line 45. A portion or all of the used neutralizing agent may be recycled through the line 46 by the pump 41. The neutralized hydrocarbons collecting in the upper portion of the settler 44 are conducted through .the line 48 to a stabilizer 50 wherein a stabilized motor fuel substantially free from isobutane is produced and withdrawn from the bottom of the stabilizer through line 5|. The isobutane is taken overhead from the stabilizer through the line 52, compressed by the compressor 53 sufficient to cause condensation when the compressed vapors are chilled in the cooler 54. The isobutane condensate is then passed through the lines 55 and 28 to the reactor ii, for reuse in the alkylation reaction.

The acid absorption step may of course be omitted, and the alkylation of the propylenecontaining mixture of hydrocarbons carried out under higher pressure to maintain the C3 hydrocarbons in the liquid phase. The present invention is particularly adaptable for alkylating the excess C3 olefins available in a plant which may already be equipped with a C4 alkylation unit which is not constructed for the higher pressures required for C3 alkylation in the absence of acid absorption. It will enable a C4 alkylation unit to be constructed at lower cost. In such case, a separate C3 alkylation unit of the required size to handle the available propylene may be added. This combination of separate C4 and C3 alkylation units also possesses the further advantage of overcoming fractionation difiiculties involved in separating propane, isobutane and normal butane from off gases resulting from the stabilization of alkylation gasoline prepared from a mixed C3 and C4 charge containing substantial proportions of both C3 and C4 hydrocarbons as they normally occur in refinery gas.

In accordance with the present invention, the mixed C3 and C4 hydrocarbons of the refinery gas are separated by fractionation into mainly an overhead C3 fraction rich in propylene and a bottom C4 fraction containing substantially all of the n-butane. The C3 fraction is supplied to the alkylation unit together with a small proportion of C4 olefin required to promote this reaction as above described, and is alkylated with strong sulfuric acid in the presence of excess isobutane in the manner set forth above. The resulting alkylation gasoline is stabilized to separate liquid products from normally gaseous products, which in this case consist essentially of propane and isobutane. These off gases may be fractionated to separate the propane overhead from isobutane bottoms, and the isobutane then recycled to the alkylation unit. The C4 fraction separated in the original fractionation as described above, may be supplied to the separate C4 alkylation unit and alkylated in the normal manner for C4 hydrocarbons. A small proportion of the C4 fraction, consisting mainly of the lighter portion thereof containing isobutane and butylones may be removed as a side stream from this main fractionator and supplied to the C3 alkylation unit in the proportion required to promote the reaction in the manner described above.

By the use of acid absorption for the Ca fraction separated in this main fractionator, a further advantage is obtained in the elimination of fractionation of the off-gases from the stabilization of the resulting alkylation gasoline. In such case, the acid absorption separates the propylene from the propane of the C3 fraction, prior to alkylation thereof; and the off-gas from the stabilization of the resulting alkylation gasoline then consists mainly of isobutane which can be recycled directly without fractionation to the C3 alkylationunit.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing. from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims. I

We claim: l. A process for the alkylationof a low boiling isoparaffin with propylene to produce high antiknock liquid hydrocarbons within the gasoline boiling range, which comprises contacting propylene with a substantial molar excess of the low boiling isoparaffin in the presence of strong sulphuric acid of alkylation strength at temperatures of -90" F. and with an added 5 to 15% by weight based on the propylene of an olefin selected from the group consisting of the butylcries and low-boiling polymers thereof, whereby low-boiling isoparaflin is alkylated with the olefins to produce the liquid hydrocarbons.

2. A process according to claim 1 in which the added olefin is isobutylene.

3. A process for the manufacture of high antiknock gasoline hydrocarbons from an olefin containing gas, the olefin content of which consists essentially of propylene, which comprises absorbing the propylene in strong sulfuric acid, separating unabsorbed gas from the propylene-acid solution, saturating additional fresh strong sulfuric acid with isobutane, introducing the propylene-acid absorption product into the additional fresh acid containing isobutane, and alkylating at a temperature of 6090 F. the propylene-acid absorption product in this mixture in the presence of excess isobutane and about 5-15% by weight based on the absorbed propylene of added olefins selected from the group consisting of butylenes and low-boiling polymers thereof,

l. whereby the isobutane is alkylated with the olefins to produce the gasoline hydrocarbons.

4. A process for the manufacture of high antiknock gasoline hydrocarbons from a refinery gas consisting essentially of a mixture of C3 and C4 hydrocarbons, which comprises fractionating the gas to separate the same into a C3 fraction containing propylene, a heavier C4 fraction containing substantially all of the normal butane and a light C4 fraction consisting mainly of isobutane and C4 olefins predominating in isobutylene and substantially free from normal butane, alkylating the separated C3 fraction at a temperature of about 0-100 F. with strong sulfuric acid of alkylation strength in the presence of excess isobutane and with the addition of a sufficient proportion of the said light C4 fraction to provide about 5-15% by weight based on the proylene of C4 olefins predominating in isobutylene, whereby the isobutane is alkylated by the olefins to produce the gasoline hydrocarbons, stabilizing the resulting alkylation products to separate normally liquid products from normally gaseous products consisting essentially of isobutane and propane, fractionating the normally gaseous products to separate isobutane from propane, and recycling separated isobutane to the alkylation reaction.

5. A process for the manufacture of high antiknock gasoline hydrocarbons from a refinery gas consisting essentially of mixed Ca and C4 hydrocarbons, which comprises fractionating the gas to separate the same into a C3 fraction containing propylene, a heavier C4 fraction containing substantially all of the normal butane, and a lighter C4 fraction containing isobutane and C4 olefins predominating in isobutylene and substantially free from normal butane, contacting the separated C3 fraction with strong sulfuric acid to absorb the propylene and separate the same from propane, alkylating the propyleneacid absorption product at a temperature of about -100 F. in the presence of strong sulfuric acid of alkylation strength with excess isobutane and a suflicient proportion of the said lighter C4 fraction to provide about 5-15% by weight based on. the absorbed propylene of said C4 olefins predominating in isobutylene, whereby the isobutane is alkylated with the olefins to produce' the gasoline hydrocarbons, separating hydrocarbon alkylation products from used acid, stabilizing the hydrocarbon alkylation products to separate normally liquid products from nor mally gaseous products consisting essentially of isobutane, and recycling separated gaseous products to the alkylation reaction.

6. A process for the alkylation of a low-boiling isoparafiin with propylene to produce high antiknock liquid hydrocarbons within the gasoline boiling range, which comprises contacting propylene with a substantial molar excess of the lowboiling isoparaflin in the presence of strong sulfuric acid of alkylation strength at temperatures of Gil- F. and with an added C4 olefinic fraction providing 5 to 15% by weight based on the propylene of C4 olefins.

7. A process according to claim 6 in which the C4 olefins of said added fraction predominate in isobutylene.

' 8. In the manufacture of high anti-knock gasoline hydrocarbons by the alkylation of isobutane with a mixture of C3 and C4 olefins in the presence of strong sulfuric acid, the improvement which comprises fractionating a hydrocarbon gas containing amixture of C3 and C4 olefins and paraffins to separate a C3 fraction containing propylene, and a light C4 fraction containing isobutane and C4 olefins predominating in isobutylene and largely free from normal butane, blending the C3 fraction with a proportion of said light C4 fraction to provide sufficient C4 olefins predominating in isobutylene to activate the alkylation of isobutane with propylene at temperatures below about F., and then a1- kylating isobutane with the resultant mixture of C3 and C4 olefins at temperatures within the range of 0-100 F. in the presence of strong sulfuric acid.

LOUIS A. CLARKE.

FRANK HENRY BRUNER.

ERNEST F. PEVERE.

GEORGE B. HATCH. 

